The study is a prospective study of bone marrow chromosome changes in preleukemia in normal human subjects. We are studying patients with refractory cytopenias and nondiagnostic bone marrow aspirates by direct bone marrow chromosome studies. Patients with suspected preleukemia have been followed by serial clinical laboratory and cytogenetic studies. Data collected on these patients have been entered into a computer to be correlated with the course of the patient. The type and incidence of chromosome abnormalities will be determined in preleukemic patients and the presence of such abnormalities related to the development of acute leukemia. The computer will be used to determine whether any clinical laboratory or cytogenetic data has proven or potential value as predictors of progression from preleukemia to leukemia. To date, 269 patients with suspected preleukemia, 151 patients with overt acute nonlymphocytic leukemia, and 152 control subjects have been studied by direct bone marrow chromosome studies. The normal subjects provide data on normal variations of the normal human marrow karyotype and are used as a basis for deciding normality and abnormality in the study patients. To date, serial cytogenetic observations have been made in 17 patients with preleukemia who have progressed to overt acute nonlymphocytic leukemia. BIBLIOGRAPHIC REFERENCES: Kyle, R.A., Pierre, R.V. and Bayrd, E.D.: Multiple myeloma and acute leukemia associated with alkylating agents. Arch. Int. Med. 135:185-192, 1975. Pierre, R.V.: Cytogenetic studies in preleukemia: Studies before and after transition to acute leukemia in 17 subjects. Blood Cells 1:163-170, 1975.